Percussion hammer bit

ABSTRACT

A drill bit for use with a percussion drilling apparatus can include an elongated body with a first end, a second end, and a longitudinal surface extending between the first and second ends. A plurality of splines extends along the longitudinal surface of the drill bit internally, and at least one of the splines has an apex, a root, and a planar surface between the apex and root. The planar surface can be oriented at an angle to a plane extending from a center of the drill bit to a midpoint of the apex. The internal splines of the hammer bit correspond to external splines in a hammer casing.

FIELD OF INVENTION

This application relates to percussive drilling equipment, and more particularly, it relates to percussion downhole hammers and hammer bits.

BACKGROUND

Percussion downhole hammers are primarily used to improve penetration rate in medium to hard formations. They can also be used effectively in drilling softer rock formations, or wherever air or foam systems can be used. The downhole hammer is less effective in unconsolidated formations such as clay, soft sand, or gravel for which roller cone bits are better suited. Bit weight, rig size, torque loads and rotation speeds can be reduced with percussion downhole hammers relative to rotary drilling. For example, a rotary bit may require 5,000 pounds of weight-on-bit (WOB) per inch of bit diameter. Downhole hammer bits require only 200 to 500 pounds of WOB per inch of bit diameter.

The light WOB required by a downhole hammer eliminates the need for a heavy string of drill collars, which in turn reduces trip time. Any excessive weight accelerates bit wear and increases the load on the rotational system.

Downhole hammers are mechanically simple; the only moving part is a piston. Compressed air drives the piston up and down, which opens and closes air intake and exhaust ports. Exhaust air vents through the bit face to carry the cuttings to the surface. By using the piston to direct the compressed air, valves are eliminated. This means fewer parts to wear out and replace, which decreases maintenance. Hammers without valves can operate at higher pressures than hammers with valves, e.g., up to 350 psi versus 150 psi, thus providing faster rock penetration with valveless hammers.

The development of the valveless hammer has produced advances in drilling speed while requiring less air volume per foot of hole drilled. The short rapid blow of the downhole hammer and the lighter weight on the bit results in good penetration rates and straight holes. When increasing the blows per minute, an accompanying increase in drill string rpm may be required. Also, when drilling softer formation, revolutions per minute (rpm) may have to be increased.

Torque loads and rotation speeds are much lower in downhole hammers than rotary bits. A rotary speed of 10 to 60 rpm allows the downhole hammer inserts to penetrate new formation after each blow. The piston drives its energy through the bit and into the formation. After fracturing occurs, the inserts are rotated to a new position. Bit rotation should also be as slow as possible to maintain a smooth operation with as little torque as possible.

Drilling speed and the ability to clean a hole using a downhole hammer is proportional to the amount of air pressure and volume used. Downhole hammers require no more air volume but higher pressures than rotary bit drilling. Of course different rock types and conditions will dramatically affect penetration rates.

As with any precision tool, downhole hammers require periodic maintenance and repair. Taking precautions in the field will decrease the amount of maintenance required, as will being aware of any pollutants to the downhole drilling system, including acid water, dirty water, dirty drill pipe, or faulty floats, which could allow water or cuttings back in the hammer during a connection.

In percussion or hammer drilling operations, a drill bit mounted to the lower end of a drill string simultaneously rotates and impacts the earth in a cyclic fashion to crush, break, and loosen formation material. In such operations, the mechanism for penetrating the earthen formation is of an impacting nature, rather than shearing. The impacting and rotating hammer bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. The borehole created will have a diameter generally equal to the diameter or “gage” of the drill bit. A typical air hammer operation begins with the hammer off bottom and the hammer bit extended out to the “blow” position. The piston is in the down position resting on the bit striking face and piston ports are not aligned with the feed tube windows. Air bypasses all timing ports and flows through the piston inside diameter (ID), out bit ports and up an annulus.

The hammer is lowered to bottom and the bit slides up in the hammer, simultaneously moving the piston up. The lower chamber ports in the piston align with the feed tube windows and the lower chamber is pressurized (or “charged”) starting the piston in the upward stroke. Once the bottom of the piston travels past the blow tube, also known as a “foot valve,” the lower chamber is able to exhaust air and/or fluids through the bit. At this point the feed tube windows are no longer aligned with the piston lower chamber ports.

Due to its momentum, the piston continues to travel upwards, aligning the upper chamber ports with the feed tube windows and charging the upper chamber. The pressure in the upper chamber overcomes and then reverses the momentum of the piston, driving it downwards. The piston travels downwards with great velocity until impacting the bit, sending its impact energy as a stress wave through the hammer bit and into the formation.

After striking the hammer bit, the piston rebounds and the cycle is initiated again. This cycling repeats until the drill string is picked-up, thereby allowing the bit to drop to the blow position, at which time the piston ports are not aligned with the feed tube and the piston will not cycle. Air hammers typically cycle from 900 to 1200 beats per minutes (BPM) in larger hammers (11″ and up) to a high of approximately 1600/1800 beats per minute in the smaller hammers (6″ and 8″ series).

In the process of percussion drilling a hole for a well, the percussion drilling assembly, which includes a hammer and bit assembly, may, if operation is other than desirable to maintain efficient drilling, instill stress riser(s) in the piston and/or bit. Stress risers may be caused by a variety of issues, such as but not limited to, galling caused by (1) lack of lubrication, (2) excessive torque, etc. When this occurs, it is inevitable that within a short period of time, because of the continued accordion like compression and relaxation of the bit and piston material caused by the continued cyclic nature of the piston striking the bit and the transfer of energy through the piston and bit to the earthen formation and the rebound of energy thru same, that the stress riser will cause a catastrophic failure of the piston or the bit or both. When a failure happens, the drilling penetration into the earth will drastically slow or will cease altogether, resulting in a “trip” out of the well, i.e., removing the entire drill string from the well. After retrieving all of the drill string, the percussion assembly must be changed, and/or the broken pieces must be retrieved from the well bore, which process is referred to as “fishing.” Thus, there is a need in the industry for a simplified and more resilient percussion hammer assembly with fewer moving parts to wear out and/or break.

SUMMARY

The present invention solves the foregoing problems by providing a percussion hammer assembly with a bit having internal splines that mate to external splines on a hammer case.

One aspect of the invention is that the drive splines of the bit are inside or on the internal area of the bit, as opposed to conventional hammer bits that have outside/external drive splines.

A second aspect of the invention is a percussion hammer assembly including a bit having internal drive splines; a bit retaining ring or retainer that, in conjunction with a locking ring, keeps the bit attached to the hammer case (or “casing”).

A feature of the invention is that the hammer is able to operate “on bottom/bit closed,” in which case air enters a lower air chamber of the hammer assembly and moves an internal piston upwards. Timing devices allow air to enter an upper chamber of the hammer assembly as air is exhausting the bottom air chamber. The upper chamber is pressurized or charged, which causes the piston to reverse direction and travel axially toward the hammer bit face. When the piston strikes the bit, the piston transfers energy through the bit and into the earthen formation. To stop operating, the hammer assembly is placed “off bottom/bit open, or extended,” which causes the piston to cease cycling and to allow air to discharge with no hammer energy transfer from the piston through the bit into a formation.

Another feature of the invention is a guide sleeve that can be integral with the hammer case or a separate member that can be inserted into the case to facilitate bottom air chamber piston timing and exhausting of air from the bottom air chamber to the external area of the bit and hammer Another feature of the invention is that the piston travels axially and delivers energy to the strike section of the bit.

Another feature of the invention is a back head/top section of the hammer that contains an air control section, e.g., a float tube/air distributor, a check valve, and a top cylinder. The back head connects to the top of the hammer case.

Another feature of the invention is that the hammer case has drive splines that are on the outside/exterior as opposed to conventional hammer cases that have a driver sub/chuck with inside/internal splines to drive/turn a bit.

Another feature of the invention is that the bit retaining rings are on the inside of the bit and outside/external of the case as opposed to conventional hammer bits in which the retaining rings are around the outside of the bit.

Another feature of the invention is that the drive splines of the case can have integral medium (welded, bonded, etc.) or medium that can be inserted between the splines of the hammer and bit (drive plates/pins, etc.) to reduce friction between the hammer bit and casing.

Another feature of the invention is that the integral medium on hammer case splines can be of material that allows the bit to travel parallel to the axis, in normal operation, with reduced possibility or complete elimination of galling of material that may cause a very high percentage of catastrophic bit failures.

Another feature of the invention is that the top part of the hammer, sometimes referred to as the “top sub,” that connects to the hammer case may be designed with either an API oilfield threaded box (female) or pin (male) connection, other types of connectors, or as a conventional mandrel section of a down hole air/fluid motor that will allow this hammer design, which is much shorter in length than conventional hammers and bits, to be used in conjunction with and as an integral part of a down hole motor for the many uses in directional drilling.

An advantage of the invention is that the cross section of bit that transfers energy from a piston strike through the bit to formation occurs in a much shorter time, allowing the energy transfer to occur much faster and breaking earthen formation more efficiently.

Another advantage of the invention is that the design of the bit removes the drive splines of the bit from the energy transfer portion of the bit head as a piston strikes the bit, thus eliminating the constant compression and release of energy from the drive splines and confining the energy transfer to the more solid bottom section of the bit. In a conventional hammer bit, the energy must travel from the strike face at the top of the bit, through the complete bit to the face and formation, and then rebound through the complete bit back to the strike face again before the next blow from the piston.

Another advantage of the invention is that the axial cross section of the bit area that transfers energy from piston contact through the bit to the formation being drilled has a length less than that of conventional hammer bits, which allows faster and more efficient energy transfer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a hammer bit having internal drive splines;

FIG. 2 is a perspective view of the outside of a hammer bit having internal drive splines and helical scallops along the entire length of the hammer bit;

FIG. 3 is a planar side view of a hammer casing having external splines;

FIG. 4 is a planar side view of an exterior surface of an internally-splined hammer bit and a locking device;

FIG. 5 is a planar side view of a bit retention member between an internally-splined hammer bit connected to a hammer casing having external splines;

FIG. 6 is a planar side view of an internally-splined hammer bit connected to a hammer casing and a mandrel of a downhole motor or a drill string; and

FIG. 7 is a sectional view of an internally-splined hammer bit connected to a hammer casing having external splines.

EMBODIMENTS

In one of many possible embodiments of the invention, a downhole percussion hammer assembly includes a hammer bit with internal splines and a hammer casing with external splines that correspond to the internal splines of the hammer bit. A conventional hammer bit has external drive splines, and percussive energy must travel from the strike face at the top of the bit all the way through the complete bit, including the drive splined area, to the face and formation, and then rebound through the complete bit to the strike face again before the next blow from the piston. The resulting energy transfer and rebound result in continuous compression and relaxation of the bit material. This accordion like effect magnifies any machining or material flaws in the hammer bit or hammer casing splines that would create a stress riser and eventually lead to a material failure. The hammer bit of the present application optionally can include an exhaust tube/blow tube that allows for bottom chamber air compression and exhausting.

FIG. 1 shows an example of one of many possible embodiments of a hammer bit 102 of the present application. The hammer bit 102 can have a body 104 and formation-impacting face 106. The body 104 is contiguous with and extends away from the face 106. One or more scallops 112 can be included on the exterior surface of the hammer bit 102. The face 106 is at the bottom of the bit 102 and can include inserts, e.g., carbon, diamond, etc., to help break and penetrate hard formations.

At the end of the bit 102 opposite the face 106, there is an opening 108 for receiving the hammer casing 302. As seen through the opening 108, the hammer bit 102 can include splines 110, also referred to as “drive splines,” along the interior surface of the hammer bit 102. The drive splines 110 of the hammer bit 102 can receive drive rotation from a drill string or mandrel of a downhole motor via the hammer casing 302. The splines 110 of the bit 102 correspond to splines 304 on the outer surface of the hammer casing 302. The hammer bit 102 optionally but preferably can include one or more scallops 112 around the circumference of the bit 102. The shape and orientation of the scallops 112 can stabilize the hammer drill assembly as the hammer bit 102 is penetrating a rock formation.

The hammer bit 102 can include a strike face 704 at or near the bottom most portion of the hammer casing 302. The hammer bit 102 internal drive splines 110 can be positioned above the strike face 704 of the bit 102. The hammer bit 102 can include a bottom bit bearing that is above, below, or adjacent to the hammer bit 102 internal drive splines 110 and above the strike face 704 of the bit 102.

FIG. 2 shows an alternative embodiment of a hammer bit 102 of the present application. The scallops 212 can be helical and extend along the entire length of the hammer bit 102 body 104. The hammer bit 102 can have extended helical scallops 212 because there are no external splines on the outer surface of the hammer bit 102. The presence of splines along the body 104 of the hammer bit 102 would prevent the scallops 212 from extending along the body 104 of the hammer bit 102. Scallops, which often are limited to the bottom-most portion of an externally-splined hammer bit, advantageously can extend along the entire length of the hammer bit 102 of the present application because the hammer bit 102 has internal drive splines 110 rather than external splines. One or more ports 220 can be included in the hammer bit 102 for dispersing fluid from the interior of the hammer bit 102.

As shown in FIG. 3, a hammer casing 302 can have external splines 304 that correspond to the internal splines 110 of the hammer bit 102. The hammer casing 302 can be externally splined to match the internal splines 110 of the hammer bit 102 to transfer rotational energy and to allow vertical travel of the hammer bit 102 parallel to the axis of assembly. This vertical or parallel to axis movement allows the hammer to operate on bottom-bit retracted, allowing air to fill a bottom air chamber, causing pistons to move up until porting allows air to fill a top chamber, and air pressure from compression of the top chamber overrides piston velocity and starts the piston down until the piston contacts the bit and transfers energy through the bit, and stops operating off bottom-causing the piston to cease cyclic action and to allow air to discharge through an annulus with no hammer energy transfer from piston to bit.

The drive splines 304 of the case 302 mate to the internal drive splines 110 of the hammer bit 102 and are on the outside/external area of the case 302 as opposed to conventional hammer cases that have a driver sub with internal splines to drive and/or turn the hammer bit. The drive splines 304 of the case 302 further can have an integral friction-reducing medium that is welded, bonded, etc., to the splines 304. Alternatively, the friction-reducing material can be separately inserted between splines 304 of the hammer case 302 and splines 110 of the hammer bit 102. Material integral to the hammer case splines 304 can be of material that allows the hammer bit 102 to travel parallel to axis in normal operation, and which reduces or eliminates galling of material that may cause the typical very high percentage of catastrophic bit failures.

A locking device 320 can be included to further secure the hammer bit 102 to the hammer casing 302. The locking device 320 can have an internal diameter that is threaded and which can be secured using matching internal threads on the hammer bit 102. A guide sleeve can be integrated as part of or inserted into the case 302, and can be used in place of a blowtube/exhaust tube to evacuate air from the bottom air chamber to an annulus. The downhole percussion hammer can further include a top bit bearing integrally connected to the locking device.

Referring to FIG. 4, there is shown a hammer bit 102 having a face 106 and a body 104. The hammer bit 102 is internally splined, and the body 104 extends away from the face 106. There is a port 220 in the face 106 of the hammer bit 102 for dispersing air and/or fluids from inside the hammer bit 102. A locking device 420 can be secured to the hammer bit 102 opposite the face 106. The locking device 420 can be positioned around the outside of the hammer casing 302 to prevent the hammer bit 102 and hammer casing 302 from separating. A bit retaining ring 510, or retainer and locking ring(s), can be included and can further keep the bit 102 freely attached to a hammer case 302, while allowing for vertical movement of the bit 102 independent of the hammer case 302 drive area. The locking ring(s) can prevent the bit from disengaging from the hammer during operation. The bit retaining ring 510 can be on the inside of the hammer bit 102 as opposed to conventional hammer bits that have the retaining rings around the outside of the bit.

FIG. 6 shows a hammer bit 102 secured to a hammer casing 302, which in turn is connected to an upstream mandrel of a downhole motor or to a drill string, both of which are represented generally at number 610. The hammer bit 102 has internal splines and includes a body 104 and a face 106, which further has a port 220 for dispersing air and/or fluids from inside the hammer bit 102. The casing 302 has external splines, represented generally at 304, that correspond to the internal splines of the hammer bit 102, and which allow the hammer bit 102 to move up and down along the longitudinal axis of the hammer assembly. A locking device 320 can be secured to the hammer bit 102 to further keep the hammer bit 102 and hammer casing 302 connected. The hammer casing 302 can be connected to a drill string 610 or to a mandrel of a downhole motor, also shown generally at 610.

Referring generally to FIG. 7, a piston 702 can deliver energy to a strike contact section 704 of a hammer bit 102. The hammer bit 102 can be connected to a hammer casing 302. The hammer bit 102 has internal drive splines 110, and the hammer casing 302 has external splines 304 that correspond to the internal splines 110 of the hammer bit 102.

The piston 702 can include internal or external exhaust timing of a bottom air chamber. The piston design and cyclic action may be altered from conventional type pistons because the energy transfer from the piston through the bit is changed significantly. Advantages include: (i) reduced piston design mass; (ii) increased piston velocity; (iii) increased piston beats per minute (BPM); (iv) reduced air consumption in relation to piston energy transfer; and (v) may allow for reduced hammer operating air pressures. A choke system can be included to allow quantity of air volume that is deemed in excess of hammer operation to bypass power phase of piston downward motion and be used to exhaust at or near the bit face to facilitate hole cleaning or broken formation evacuation.

The hammer assembly can include a back head/top section assembly but it preferably includes an (1) air control valving/timing section, (2) check valve and (3) top cylinder. The back head connects to the top of the hammer case. Back head/top sub/top part of hammer that connects to case of hammer, can be designed with either an API oilfield threaded pin (male) or box (female) connection, other means to connect the back head/top sub/top part to the hammer case, or as the mandrel, bottom section of a down hole air/fluid motor, to allow this unconventional hammer design, which is shorter in length than conventional hammers and bits this lends itself to be more user friendly and to be used in conjunction with and as an integral part of a down hole motor for many uses in directional drilling. An air distributor-control rod can distribute air to the piston and upper air chamber of the hammer assembly.

CONCLUSION

While various preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings herein. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the apparatus disclosed herein are possible and within the scope of the invention. Accordingly, the scope of protection is not limited by the description set out above. 

What is claimed is:
 1. A downhole percussion hammer assembly, comprising: a hammer bit having internal splines; a generally cylindrical hammer casing having external splines corresponding to the splines of the hammer bit; a bit retention mechanism external to the hammer casing, and connected to the hammer bit internally; a locking device located externally to the hammer casing, and internally to the hammer bit; a friction reducing agent between the hammer casing splines for reducing friction between the hammer casing splines and the bit splines; a piston for delivering percussive force to the hammer bit; a top sub assembly comprising a top cylinder having an air distributor for timing air flow to upper and lower air chambers of the percussion hammer assembly, wherein the top sub assembly is secured to the hammer casing.
 2. The downhole percussion hammer assembly of claim 1, further comprising one or more ports in the hammer bit for allowing air or fluid to disperse from inside the percussion hammer assembly.
 3. The downhole percussion hammer assembly of claim 1, further comprising one or more helical scallops along a length of an exterior surface of the hammer bit.
 4. The downhole percussion hammer assembly of claim 1, wherein the top sub assembly is secured to the hammer casing and to an upstream drill string.
 5. The downhole percussion hammer assembly of claim 1, wherein the top sub assembly is connected to the hammer casing and to a bottom mandrel of a downhole motor.
 6. A downhole percussion hammer assembly, comprising: a hammer bit having internal splines; and a hammer casing having external splines corresponding to the splines of the hammer bit.
 7. The downhole percussion hammer assembly of claim 6, further comprising a bit retention mechanism external to the hammer casing, and connected to the hammer bit internally.
 8. The downhole percussion hammer assembly of claim 6, further comprising a locking device located externally to the hammer casing, and internally to the hammer bit.
 9. The downhole percussion hammer assembly of claim 6, further comprising one or more ports in the hammer bit for allowing air or fluid to disperse from inside the percussion hammer assembly.
 10. The downhole percussion hammer assembly of claim 6, further comprising a friction reducing agent between the hammer casing splines for reducing friction between the hammer casing splines and the bit splines.
 11. The downhole percussion hammer assembly of claim 6, further comprising a top sub assembly comprising a top cylinder having an air distributor for timing air flow to upper and lower air chambers of the percussion hammer assembly, wherein the top sub assembly is secured to the hammer casing.
 12. The downhole percussion hammer assembly of claim 11, wherein the top sub assembly is an integral part of a bottom mandrel of a downhole motor.
 13. The downhole percussion hammer assembly of claim 6, further comprising a piston for delivering percussive force to the hammer bit.
 14. The downhole percussion hammer assembly of claim 6, wherein the internal splines of the hammer bit are parallel to a longitudinal axis of the bit.
 15. The downhole percussion hammer assembly of claim 8, wherein the locking device is a bit retaining ring.
 16. The downhole percussion hammer assembly of claim 6, wherein the hammer bit further comprises one or more helical scallops along a length of an exterior surface of the hammer bit.
 17. The downhole percussion hammer assembly of claim 6, wherein the percussion hammer further comprises an air chamber having a timing mechanism for allowing exhaust to escape a bottom chamber either internally through a blow tube or externally through a guide sleeve.
 18. A method of drilling a hole using a downhole percussion hammer assembly, comprising: securing a top sub section of a hammer casing to a mandrel of a downhole motor or to a section of drill string; connecting a hammer bit to the hammer casing, wherein the hammer bit has internal drive splines and the hammer casing has external splines that correspond to the internal drive splines of the hammer bit; and applying repeated percussive force to the hammer bit with a piston contained within the percussion hammer assembly, wherein upper and lower portions of the hammer assembly are energized and thus power the piston by air or fluid pressure changes and flow into and out of the upper and lower chambers of the hammer assembly. 